Redox amplification processes have been described, for example in British Specifications Nos. 1,268,126; 1,399,481; 1,403,418; and 1,560,572. In such processes color materials are developed to produce a silver image (which may contain only small amounts of silver) and are treated with a redox amplifying solution (or a combined developer/amplifier) to form a dye image.
The developer/amplifier solution contains a color developing agent and an oxidizing agent which will oxidize the color developing agent in the presence of the silver image which acts as a catalyst.
Oxidized color developer reacts with a color coupler to form the dye image. The amount of dye formed depends on the time of treatment or the availability of the color coupler and is less dependent on the amount of silver in the image than is the case in conventional color development processes.
Examples of suitable oxidizing agents include peroxy compounds including hydrogen peroxide and compounds which provide hydrogen peroxide, e.g., addition compounds of hydrogen peroxide such as perborates, and addition compounds of hydrogen peroxide with urea. Other oxidizing agents include cobalt (III) complexes including cobalt hexammine complexes; and periodates. Mixtures of such compounds can also be used.
In color photography development (whether redox or conventional) it is necessary at an appropriate stage to remove the silver image, which if left behind, would darken the dye image. Also it is necessary to remove unused silver halide because it darkens on exposure to light.
To remove the silver it has been previously proposed to convert it to silver halide with a suitable oxidizing agent known in the art as a bleach such as potassium ferricyanide or ferric iron complexed with ethylenediaminetetraacetic acid acting in the presence of potassium bromide. The two steps may be combined using a solution called a beach-fix or blix.
In the case of a bleach-fix employed after redox amplification, the solution only needs small amounts of iron (III) and thiosulfate because they have only small amounts of silver to remove.
It has been reported previously that when a bleach-fix step in which ferric iron is the oxidizing agent immediately follows redox development that dye formation continues in some layers. This is probably caused by a catalytic action of the iron in the bleach fix. This continued dye formation results in a staining of the image.
U.S. Pat. No. 5,354,647 discloses a method by which the staining can be reduced or eliminated by including a high concentration of sulfite in the bleach-fix solution. However, when the bleach-fix has become seasoned, particularly when low replenishment rates are used, the staining reappears and it has been previously proposed to include a stop or stop-fix between the developer/amplifier and the bleach-fix.
This has the disadvantage in making the processor larger and the overall process time longer.